linux-kernel - [PATCH V32 21/27] Lock down tracing and perf kprobes when in confidentiality mode

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Date:   Wed,  3 Apr 2019 17:32:43 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        linux-api@...r.kernel.org, luto@...nel.org,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Matthew Garrett <mjg59@...gle.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        davem@...emloft.net, Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH V32 21/27] Lock down tracing and perf kprobes when in
 confidentiality mode

From: David Howells <dhowells@...hat.com>

Disallow the creation of perf and ftrace kprobes when the kernel is
locked down in confidentiality mode by preventing their registration.
This prevents kprobes from being used to access kernel memory to steal
crypto data, but continues to allow the use of kprobes from signed
modules.

Reported-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Matthew Garrett <mjg59@...gle.com>
Cc: Naveen N. Rao <naveen.n.rao@...ux.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Cc: davem@...emloft.net
Cc: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_kprobe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index d5fb09ebba8b..5c70acd80344 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -420,6 +420,9 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 {
 	int i, ret;
 
+	if (kernel_is_locked_down("Use of kprobes", LOCKDOWN_CONFIDENTIALITY))
+		return -EPERM;
+
 	if (trace_probe_is_registered(&tk->tp))
 		return -EINVAL;
 
-- 
2.21.0.392.gf8f6787159e-goog